Thermostatically controlled space-heating and cooling systems are well known in the art. Typical examples are hot-water baseboard heating systems, forced-air cooling systems, and infra-red heating systems. In general, virtually all space-heating and cooling systems in use today have a constant thermal output, which output is selected to provide maximum heating or cooling on those days where the extreme temperature is reached for that area. Most systems which are constructed in the above manner have inherent disadvantages when extremes of temperature are not present. For example, if the system is designed for a temperature differential of 80.degree. F. (70.degree. F. indoor temperature and a -10.degree. F. outdoor temperature), and if there is only a 30.degree. F. difference between the desired temperature inside and the actual temperature outside (40.degree. F.) the system will tend to overshoot, have poor thermal response, have substantially oversized capacity, and poor thermal efficiencies.
As the present invention has been developed for radiant-heating systems, such systems will be described in greater detail below. However, it should be understood that the principles of this invention may be applied to other heating or cooling systems.
When heating an enclosure with a radiant-heating system, such as the type sold under the trade name Co-Ray-Vac by Roberts-Gordon, Inc. of Buffalo, N.Y., it should be recognized that the greatest heating efficiencies are achieved when the unit is operating at design capacity. Thus, in the example given above, the Co-Ray-Vac system when installed in accordance with design specifications, is fully condensing at -10.degree. F. outside temperature. However, when operating at 40.degree. F. outside temperature, although the system will still be fully condensing, it will tend to overshoot when heating, it will have substantially oversized capacity, and will inherently have poor fuel utilization efficiencies due to short cycles and large temperature swings.
It should also be apparent that with such a system that there are constructional costs incidental to having the system fully condensing at design temperatures, where the system is most fuel efficient. However, the condensing radiant pipe or tail pipe, while needed to be of a greater length when the system is operating at its maximum temperature extreme, need not be so long when the system is operating at a temperature considerably less than the extreme. In summary, it should be noted that such systems, when designed to maximum temperature ranges, operate most efficiently only during a very small fraction of the time and also require greater capital costs of installation.